1. Field of the Invention
This invention relates to radiation curable diluents which are lower alkyl ether (alkoxy) acrylates and methacrylates of particular alkoxylated and non-alkoxylated polyols and to radiation curable compositions containing same.
2. Description of the Prior Art
Radiation curable or hardenable compositions, particularly for coating applications, are known in the art. In view of the restrictions on solvent content in the atmosphere, increasing efforts have been made to provide completely polymerizable systems which do not contain any volatile components, but instead consist of constituents which form either the whole or a part of the hardened film itself.
Although radiation curable oligomers and polymers form the backbone of a radiation curable coating, they cannot normally be used alone because of their high viscosity and poor application properties. Viscosity reduction is usually accomplished by use of reactive monomers. These not only act as diluents for the system, but also copolymerize with the oligomers and polymers and contribute to the final properties of the cured film. Examples of reactive monomers, also referred to as radiation curable diluents, are multifunctional acrylates and methacrylates of alkoxylated and non-alkoxylated polyols. Reference is made to the following U.S. Pat. Nos. for examples of same.
3,594,410--Cohen et al, Jul. 20, 1971 PA1 3,857,822--Frass, Dec. 31, 1974 PA1 4,058,443--Murata et al, Nov. 15, 1977 PA1 4,088,498--Faust, May 9, 1978 PA1 4,177,074--Proskow, Dec. 4, 1979 PA1 4,179,478--Rosenkranz et al, Dec. 18, 1979 PA1 4,180,474--Schuster et al, Dec. 25, 1979 PA1 4,382,135--Sinka et al, May 3, 1983 PA1 G=Good-no marking of film PA1 F=Fair-slight marking PA1 P=Poor-penetration and tearing of film PA1 G=Good--85-100% PA1 F=Fair--less than 85%
Conventional multifunctional acrylates and methacrylates such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate and 1,6-hexanediol diacrylate and dimethacrylate were the major reactive monomers developed and introduced in the 1970's for use in radiation curable coatings. Although they exhibited several of the desired characteristics of an ideal monomer, there were many problems and limitations associated with their use.
Trifunctional types, e.g., trimethylolpropane triacrylate and pentaerythritol triacrylate, were fast curing but produced brittle films with severe shrinkage and poor adhesion to a variety of substrates. Moreover, their higher intrinsic viscosities contributed to poorer solvency and inadequate viscosity reduction characteristics which limited their use in many applications. Difunctional types, e.g., 1,6-hexanediol diacrylate and dimethacrylate exhibited superior viscosity reduction but poor or slower cure response. Many of these monomers also posed serious skin irritancy problems in compounding and processing of the coatings.
Thus, a need was shown for reactive monomers with fast cure response (high reactivity), low intrinsic viscosity, low shrinkage and excellent solvating or viscosity reducing properties.